The present invention relates to an inkjet head for an inkjet printing apparatus, and more particularly, an inkjet head provided with a piezoelectric element unit having a unit matrix of a plurality of piezoelectric devices.
Conventionally, an inkjet head employing a laminated type piezoelectric actuator has been known. An example of such an inkjet head is disclosed in U.S. Pat. No. 5,402,159, teachings of which are incorporated herein by reference. The inkjet head according to the above-described patent, a plate type piezoelectric actuator, which includes a plurality of laminated piezoelectric sheets, is adhered onto a cavity plate formed with a plurality of nozzles and corresponding pressure chambers.
In Japanese Patent Publications of examined applications No. HEI 2-4429 or No. HEI 7-67803, an inkjet head having a cavity plate provided with rhombic pressure chambers is disclosed.
In Japanese Patent No. 2,752,843, a thermal inkjet head having a width same as the width of a recording sheet is disclosed. The inkjet head is configured such that a plurality of rectangular-shaped printing head sub-units (i.e., piezoelectric device unit) are arranged on a stick type support. Specifically, the plurality of sub-units are arranged in a zigzag pattern along the stick type support, with a part thereof overlapped in the sheet width direction. When an image is printed using the head, a sheet is fed in a direction perpendicular to the longitudinal direction of the stick type support.
According to the configuration of the inkjet head disclosed in the Japanese Patent 2,752,843, a plurality of sub-units are linearly arranged, with spaced by a certain amount with each other, along the longitudinal direction of the stick type support, and a pair of the linearly arranged sub-units are aligned in a sheet feed direction (i.e., a direction perpendicular to the longitudinal direction of the stick type support), such that the sub-units arranged on the different lines slightly overlap in the longitudinal direction. Due to this configuration, a relatively large room for accommodating the sub-units is required. With the above configuration, a utility efficiency is relatively high although the slightly overlapped portions exist. However, since the length of the entire area of the sub-units in the sheet feed direction is relatively large, a position where the ink is ejected from the inkjet head to the sheet is widened in the sheet feed direction. It is required that the position where the ink is ejected is as flat as possible, a platen roller or the like is required to have a larger diameter. Accordingly, components around the inkjet head, including sheet feeding mechanisms, as well as the inkjet head itself are relatively large, which makes it difficult to downsize the entire printing apparatus.
The present invention is advantageous in that an inkjet head and sheet feeding mechanisms can be downsized, and accordingly, a compact inkjet head which is elongated in the sheet width direction can be provided.
According to an embodiment of the invention, there is provided an inkjet head employed in an inkjet printing apparatus, which is provided with a main body provided with a printing surface having a substantially rectangular elongated shape, and a plurality of piezoelectric modules. Each of the piezoelectric modules has a substantially trapezoidal shape, and is provided with a plurality of piezoelectric unit structures. The plurality of piezoelectric modules are arranged along a longitudinal direction of the printing surface such that upper base of the trapezoidal shape is located at a central portion in a direction perpendicular to the longitudinal direction. Further, the plurality of piezoelectric modules are oriented in opposite directions alternately in the direction perpendicular to the longitudinal direction.
With this configuration, the inkjet head can be downsized, and thereby a space occupied by the inkjet head and sheet feed mechanisms employed in the inkjet printing apparatus can be reduced.
Optionally, the trapezoidal shape may be formed such that a first angle, which formed by the lower base and a first side connecting one side of the upper base and one side of the lower base, is different from a second angle, which formed by the lower base and a first side connecting the other side of the upper base and the other side of the lower base.
In a particular case, the first angle may be greater than the second angle, and the plurality of piezoelectric modules may be arranged on the printing surface such that the end sides of the arranged plurality of piezoelectric modules are the first sides.
With this arrangement, the utility efficiency of the piezoelectric structures is improved.
Optionally, at least two adjoining piezoelectric modules may be arranged such that the second sides thereof face each other with a predetermined distance therebetween.
Further optionally, the main body may be defined with a plurality of pressure chambers located at positions corresponding to the plurality of piezoelectric unit structures and manifolds through which ink is supplied to the plurality of pressure chambers. The manifolds may include a first manifold and a second manifold at an area defined by the second sides of the trapezoidal shapes of each adjoining two piezoelectric modules. In this case, the first manifold and second manifold may be spaced by a predetermined distance at the area defined by the second sides of each adjoining two piezoelectric modules.
With this configuration, manifolds capable of supplying sufficient amount of ink and still having sufficient mechanical rigidity can be realized.
Further optionally, the inkjet head may include ink inlets through which ink is supplied to the inkjet head, the ink inlets being arranged at portions corresponding to areas each surrounded by three adjoining piezoelectric modules.
In a particular case, all the trapezoidal shape may be identical. Accordingly, fabrication process for the piezoelectric modules can be simplified, which reduces the fabrication cost.